Quantitative Precipitation Forecast
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FOUS30 KWBC 180831
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT MON MAY 18 2015

...VALID 12Z MON MAY 18 2015 - 12Z TUE MAY 19 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE 62H 25 WSW PSN 40 NW SHV 35 W LLQ 20 NE LLQ 40 SSW UTA
20 SE OLV 20 NNE TUP 10 W GTR 35 W MEI 20 N MCB 45 NW BTR
25 NW LCH 10 SSE SGR 15 NNE 62H.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SSW PUB 30 N LAA 40 WSW GCK 15 NE PYX 35 SSE HHF 20 SSW CDS
30 E LBB 35 WNW LBB 15 NNE CVN 40 ESE LVS 20 WSW RTN 20 SSW PUB.


...EAST TX/LOWER MS VALLEY...

A BROAD SLIGHT RISK HAS BEEN PLACED FROM JUST WEST OF COLLEGE
STATION...TX INTO THE LOWER MS VALLEY. DECIDED TO EXTEND THIS
OUTLOOK INTO NORTHERN MS GIVEN THE SIGNIFICANTLY LOW FFG VALUES
FROM THE ONGOING NOCTURNAL CONVECTION. HOWEVER...MUCH OF THE
ACTION WILL TURN BACK TOWARD THE EASTERN SIDE OF TX AS A SHORTWAVE
SEEN ON WATER VAPOR IMAGERY MOVING THROUGH NORTH-CENTRAL MX.
STRONG DIFFLUENCE IN ADVANCE OF THIS IMPULSE HAS SPARKED A
WEST-TO-EAST ORIENTED BATCH OF CONVECTION. THE LAST FEW RUNS OF
THE HRRR HAVE DONE A POOR JOB RESOLVED THUNDERSTORM INITIATION.
THE 07Z HRRR BELIEVED THE AREA WAS CAPPED WHICH DID NOT APPEAR TO
BE THE CASE. THE RENEWED CONVECTION HAS FIRED ACROSS NORTHEASTERN
TX STRETCHING EASTWARD INTO NORTHERN LA. ANOTHER SURGE OF HIGH
PWAT/THETA-E AIR IS EXPECTED THIS MORNING WHICH SHOULD RAMP UP
ACTIVITY ACROSS THE REGION. NEARLY ALIGNED LOW-LEVEL INFLOW TO THE
MEAN CLOUD-BEARING FLOW SUPPORTS A PERIOD OF
TRAINING/BACKBUILDING. CONVECTION SHOULD DRIFT TOWARD THE EAST
WITH REGENERATION ALONG THE INFLOW TO THE WEST. WPC CURRENTLY HAS
MPD #0100 OUT FOR THE AFFECTED AREA UNTIL 14Z. THE HIGH-RESOLUTION
GUIDANCE HAS A PRETTY STRONG SIGNAL OF THIS HEAVY RAINFALL
EVOLVING BUT VARY IN PLACEMENT.


...SOUTHERN ROCKIES/SOUTHERN HIGH PLAINS/TX PANHANDLE...

AS THE UPPER TROF MOVING INTO CA ADVANCES FARTHER INLAND...THE
UPPER FLOW WILL BECOME INCREASINGLY MORE DIFFLUENT ACROSS THE
SOUTHERN ROCKIES/HIGH PLAINS REGION. BY 19/0000Z...THE LLJ IS
FORECAST TO PICK UP STEAM WITH 2O TO 30 KNOT SOUTHEASTERLY FLOW
IMPINGING ON THE LOCAL TERRAIN OF NM/CO. THIS SURGE OF UPSLOPE
FLOW IN CONJUNCTION WITH STRONG MID/UPPER FORCING SUPPORT FAIRLY
HEAVY RAINFALL ACROSS EASTERN NM INTO SOUTHEASTERN CO.
ADDITIONALLY...STRONG CONVERGENCE IS NOTED AT THE SURFACE WHICH
APPEARS TO BE JUXTAPOSED ON A STRONG MOISTURE GRADIENT/DRY LINE.
THIS ACTIVITY IS EXPECTED TO MOVE OFF THE TERRAIN AND REACH THE
HIGH PLAINS DURING THE OVERNIGHT HOURS. HEFTY RAINFALL RATES
COMBINED WITH POTENTIALLY SLOW CELL MOTIONS SUPPORT A RISK FOR
FLASH FLOODING. A VAST MAJORITY OF THE CONVECTION ALLOWING MODELS
FAVOR HEAVY AMOUNTS IN THE THREAT AREA...ALBEIT WITH SOME
SPATIO-TEMPORAL DIFFERENCES.


...SOUTHERN NY...

AN UPPER RIDGE CURRENTLY STRETCHING ALONG THE ENTIRE EXTENT OF THE
EASTERN U.S. WILL BREAK DOWN IN RESPONSE TO UPSTREAM HEIGHT FALLS.
AHEAD OF THE ADVANCING UPPER TROF...THE SOUTHWESTERLY MID-LEVEL
FLOW IS EXPECTED TO PICK UP SOME SPEED WITH MODELS DEPICTING 25 TO
30 KNOT WINDS OVERSPREADING THE REGION. THIS WOULD AT LEAST
SUPPORT BETTER ORGANIZATION IN INDIVIDUAL STORM STRUCTURES ACROSS
THE STATE. MOISTURE ADVECTION WILL NOT BE AN ISSUE AS ABOVE 1.50
INCH PWATS LIFT NORTHWARD AHEAD OF THE SHORTWAVE TROF. EXPECT
CONVECTION WILL BE DRIVEN BY DIURNAL HEATING WITH INSTABILITY
RISING INTO THE 500 TO 1000 J/KG RANGE IN THE AFTERNOON. THIS
SHOULD ALLOW WIDESPREAD CONVECTION TO AFFECT THE UPPER
MID-ATLANTIC WITH STORM MOTIONS AROUND 5 KNOTS TOWARD THE
EAST-SOUTHEAST. THESE SLOWER CELL MOTIONS COMBINED WITH LOWER FFG
VALUES AFFORDED A THREAT AREA ON THE LATEST EXCESSIVE RAINFALL
FORECAST.



RUBIN-OSTER
$$




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